Concentrated UV light curing of adhesive for pivot applications

ABSTRACT

A device for curing an obscured photosetting compound in a subassembly part has a base for supporting the assembly and a plate mounted to the base. The plate has a lens that concentrates UV light into a narrow slit in the assembly to quickly cure the compound. In an alternate version, the plate has a parabolic opening with a mirrored surface for gathering the UV light. A third version of the invention uses a rotatable fixture to position the assembly beneath a UV laser light source to cure the compound.

This is a Division of application Ser. No. 09/350,080 filed Jul. 8,1999, now U.S. Pat No. 6,296,734.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates in general to curing photosetting adhesives andin particular to devices and methods for curing photosetting adhesivesin a pivot cartridge assembly with concentrated UV light.

2. Background Art

Referring to FIG. 1, an information storage system comprising a harddisk drive 11 is shown. Drive 11 has a base 13 containing a plurality ofstacked, parallel magnetic disks 15 (one shown) which are closely spacedapart. Disks 15 are rotated by a motor located therebelow about acentral drive hub 17. An actuator 21 is rotatably mounted to base 13about a pivot assembly 23. A controller 25 is mounted to base 13 forselectively moving actuator 21 as will be described below.

Actuator 21 has a mounting support 27, a pair of parallel, cantileveredload beams or suspensions 29 extending from mounting support 27, and ahead gimbal assembly 31 having at least one magnetic read/write headsecured to each suspension 29 for magnetically reading data from ormagnetically writing data to disks 15. Suspensions 29 have a spring-likequality which biases or maintains them in parallel relationship relativeto one another. A motor assembly 33 having a conventional voice coilmotor is also mounted to pivot assembly 23 opposite head gimbalassemblies 31. Movement of actuator 21 (indicated by arrows) moves headgimbal assemblies 31 radially across tracks on the disks 15 until theheads on assemblies 31 settle on the target tracks.

During operation (FIG. 2), bearings 35 inside pivot assembly 23 emit oilvapor and aerosol droplets of grease which are a potential source ofcontamination in the disk drive. Reducing this type of contamination isimportant to improve the reliability of disk drives. In pivot assembly23, a photosetting, anaerobic adhesive 37 is used to bond and seal therings of the bearings 35 to a stationary housing 39 and an internalpivot shaft 45. Some adhesive 37 is located in the very small,circumferential gaps 46, 48 (approximately one to ten microns each)which extend between each bearing 35, and shaft 45 and housing 39,respectively. A hole 40 extends through the side of housing 39 into itsinterior and is used for mounting purposes.

Typically, the adhesive 37 is cured by passing the assembled pivots 23under a UV light 41. However, due to geometrical constraints, such asthe opaque flange 43 on the pivot shaft 45, access to adhesive 37 isseverely limited. In addition, the small size of gaps 46, 48 makesaccess to them severely limited. Most of the emitted light 41 reflectsoff the pivot and oven surfaces with few UV rays penetrating gaps 46, 48and the narrow slit or space 47 (approximately 0.1 mm in width) betweenthe perimeter of flange 43 and the inner diameter of housing 39. Thisresults in joints with uncured adhesive and lower bond strengths. Whenthe pivot 23 is later subjected to file operating temperatures, theuncured adhesive will outgas from parts and may also propagate cracks inthe bond, which can lead to pivot failure.

To solve this problem, pivot manufacturers have increased the time thepivots are exposed to the UV light to ensure that the adhesive hassufficiently cured. Unfortunately, this solution requires more power andlonger process times which result in increased manufacturing costs andprocess inefficiencies.

Therefore, it is a feature of the present invention to provide improvedmethods for directing UV light to the less accessible portions of pivotsto provide a completely cured bond. It is another feature of the presentinvention to provide decreased manufacturing costs and cycle times forprocessing pivots.

SUMMARY OF THE INVENTION

A device for curing an obscured photosetting compound in a subassemblypart has a base for supporting the assembly and a plate mounted to thebase. The plate has a lens that concentrates UV light into a narrow slitin the assembly to quickly cure the compound. In an alternate version,the plate has a parabolic opening with a mirrored surface for gatheringthe UV light. A third version of the invention uses a rotatable fixtureto position the assembly beneath a UV laser light source to cure thecompound.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features, advantages and objects of theinvention, as well as others which will become apparent, are attainedand can be understood in more detail, more particular description of theinvention briefly summarized above may be had by reference to theembodiment thereof which is illustrated in the appended drawings, whichdrawings form a part of this specification. It is to be noted, however,that the drawings illustrate only a preferred embodiment of theinvention and is therefore not to be considered limiting of its scope asthe invention may admit to other equally effective embodiments.

FIG. 1 is a top schematic view of a prior art hard disk drive.

FIG. 2 is a sectional side view of a pivot assembly in the disk drive ofFIG. 1.

FIG. 3 is a top isometric view of a first embodiment of a device forcuring adhesive in the pivot assembly of FIG. 2.

FIG. 4 is a sectional side view of the pivot assembly of FIG. 2 mountedin the device of FIG. 3.

FIG. 5 is a sectional side view of the pivot assembly of FIG. 2 mountedin a second embodiment of the device of FIGS. 3 and 4.

FIG. 6 is a top isometric view of a third embodiment of the device ofFIG. 3.

FIG. 7 is a sectional side view of the pivot assembly of FIG. 2 mountedin the device of FIG. 6.

FIG. 8 is an isometric view of a fourth embodiment of the device of FIG.3.

FIG. 9 is a sectional view of the pivot assembly of FIG. 2 undergoing afifth method for curing adhesive.

FIG. 10 is a schematic, isometric view of a sixth embodiment of thedevice of FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 3 and 4, a first embodiment of a device 51 forfacilitating the curing of photosetting substances is shown. Device 51comprises a base 53 with a plurality of recesses 55 (one shown) forclosely receiving the lower ends of pivot assemblies 23. Device 51 has aplate 57 with a plurality of alignment pins 59 mounted thereto whichextend downward from the lower surface of plate 57. The length of pins59 is selected to position plate 57 at a precise distance above theupper end of assemblies 23, and corresponds to the focal length of lens63. The lower end of each pin 59 is received in a socket 61 in the uppersurface of base 53. Pins 59 and sockets 61 may engage one anotherthrough smooth sliding contact, threads, or other joining means.

Plate 57 has a plurality of semi-toroidal lenses 63 (one shown forsimplicity). Lenses 63 may be integrally formed with plate 57 or affixedthereto. Each lens 63 is a glass, plastic, or otherwise UV-transparentmaterial for concentrating UV light 65 from a light source 66. The light65 incident on its convex surface is directed vertically downward tospecific locations on one assembly 23 located immediately therebelow. Inthe embodiment shown, lenses 63 have a central opening 64 foraccommodating the upper end of assembly 23. As shown in FIG. 4, lens 63focuses light 65 into the narrow space 47 between flange 43 and housing39. Space 47 is only about 0.1 mm wide, but the intense burst of light65 quickly cures the adhesive 37 located inside assembly 23. Whenassembly 23 is configured with the flange geometry 43 shown, the primarytarget for lens 63 is the adhesive 37 at or near gap 48 between theupper bearing 35 and housing 39. However, some secondary curing willalso occur at or near gap 46. With a different flange geometry (e.g.relocating space 47 radially inward, closer to gap 46), it should beapparent that the curing of adhesive 37 at gap 46 would be even morethorough.

Referring now to FIG. 5, a second embodiment of the invention is shownas device 71. Device 71 is very similar to device 51, except that it isdesigned to cure adhesive 37 on both ends of assembly 23. Device 71 hasan upper plate 73, a parallel lower plate 75, and a fixture 76 (shownschematically) for supporting assemblies 23 therebetween. Plates 73, 75are joined together with a plurality of alignment pins 77.

Each plate 73, 75 has a plurality of semi-toroidal, UV-transparentlenses 79, 81, respectively (one shown on each plate). Lenses 79, 81 areorganized in vertically aligned pairs for concentrating UV light 83 froma light source 84. The light 83 incident on the convex surfaces oflenses 79, 81 is directed toward one assembly 23 that is selectivelypositioned on a fixture (not shown) between them. Lenses 79, 81 have acentral opening for accommodating the upper and lower ends of assembly23. Lenses 79, 81 focus light 83 into the narrow space 47 and the openlower end of assembly 23, to quickly cure the adhesive 37 located in ornear gaps 46, 48 between bearings 35 and assembly 23 at both endssimultaneously.

A third embodiment of the invention is shown as device 91 in FIGS. 6 and7. Device 91 is most similar to device 51 and comprises a base 93 with aplurality of recesses 95 (one shown) for closely receiving the lowerends of pivot assemblies 23. Device 91 has a thick plate 97 with aplurality of alignment pins 99 which extend downward to base 93.

Plate 97 also has a plurality of generally parabolic openings 101 (oneshown) with a central convex hub 103. The surfaces of openings 101 andhub 103 are mirrored or highly reflective for gathering and focusing UVlight 105 from a light source 107. Light 105 is redirected from manydifferent angles downward into the narrow space 47 in assembly 23. Thefocused light 105 quickly cures the adhesive 37 located in gaps 46, 48between the upper bearing 35 and assembly 23. When assembly 23 isconfigured with the flange geometry 43 shown, the primary target foropening 101 is gap 48. However, some secondary curing will also occur ator near gap 46. With a different flange geometry, it should be apparentthat the curing of adhesive 37 at gap 46 would be even more thorough.Note that each of the lenses 79, 81 in the embodiment of FIG. 5 can bereadily replaced with an opening 101, as shown and described for device91, to cure adhesive 37 on both ends of assembly 23 simultaneously.

Referring now to FIG. 8, a fourth embodiment of the invention is shownas device 111. Device 111 comprises a movable base or fixture 113 with aplurality of positions 115 which each support a pivot assembly 23. Inthe embodiment shown, fixture 113 is a plate and positions 115 arerecesses that releasably grip the exterior of assemblies 23.

A UV light source 117 is spaced apart from fixture 113 and projectsconcentrated UV light 119 into spaces 47 and gaps 46, 48 in assemblies23. Preferably, rotating mirrors, prisms, or laser beam splitters areused to focus UV laser light in a circular pattern as shown. Fixture 113is then pivoted, rotated or incremented in the direction shown with amotor to align the next assembly 23 for UV exposure by light source 117.The focused light 119 quickly cures the adhesive 37 located beneathspaces 47 and in gaps 46, 48. Note that a second light source 117 couldbe readily mounted on the opposite side of fixture 113 in order to curethe adhesive 37 on the lower ends of assemblies 23.

A fifth embodiment of the invention is shown in FIG. 9. In this version,one end of a tube 121 extending from a UV light source 123 is insertedinto the mounting hole 40 in the side of a pivot assembly 23. Tube 121projects concentrated UV light 125 into the interior of assembly 23 forcuring the adhesive 37 used to bond bearings 35 to shaft 45 and housing39. The interior of assembly 23, including the outer surface of shaft 45and the inner surface of housing 39 are smooth, polished metal tofurther enhance the intensity of the light 125 incident on the adhesive37. Since this version is primarily suited for curing adhesive 37located in the interior of assembly 23 between bearings 35, it isdesigned to be used in conjunction with any of the preceding versions ofthe invention which are primarily for 20 curing the adhesive 37 in ornear gaps 46, 48.

Referring now to FIG. 10, a sixth embodiment of the invention is shownas device 131. Device 131 is similar to device 111 and comprises afixture 133 which is pivotable about an axle 135 and has a pair ofsupport pins 137 for engaging the upper and lower ends of a pivotassembly 23. A bias member 139, such as a spring, is used to urgefixture 133 and its assembly 23 into engagement with a rotary mechanism141 which rotates in the direction shown. In the embodiment shown,mechanism 141 is a drive wheel located adjacent to fixture 133 and has arubber belt 143 extending around its circumference for engaging thehousing 39 of assembly 23.

A UV light source 145 is axially spaced apart from fixture 133 andassembly 23. Light source 145 projects a concentrated UV light 147, suchas a single laser beam, into space 47 in assembly 23 as shown. Althoughfixture 133 is stationary during this operation, mechanism 141 rotatesassembly 23 in the direction shown. The entire circumferential length ofspace 47, and, thus, adhesive 37 in gaps 46, 48, is exposed to light 147which cures adhesive 37. Note that a second light source 145 could bereadily mounted on the opposite side of fixture 133 in order to cure theadhesive 37 on the lower end of assembly 23.

The invention has significant advantages. The various devices andmethods described for curing obstructed photosetting compounds canreduce curing cycle times by over 50% and decrease production costs.Even hard to reach areas of an assembly can be readily accessed with theinvention. The narrow slit between the opaque members of the assembliespermit just enough UV light to enter to cure the photosetting adhesive.Since the light is concentrated, the adhesive can also be cured with asingle “shot” of light rather than being exposed to UV light in an ovenfor a duration of time.

While the invention has been shown or described in only some of itsforms, it should be apparent to those skilled in the art that it is notso limited, but is susceptible to various changes without departing fromthe scope of the invention. In addition, each of these design is alsoapplicable to disk drive spindle motors.

We claim:
 1. A device for curing a photosetting substance inside anassembly having first and second components and upper and lower endswith openings, the photosetting substance being located at interfacesbetween the components adjacent to the openings, the device comprising:a rotary mechanism having a drive wheel and a belt extending around acircumference of the drive wheel for engaging one of the components ofthe assembly; a fixture having a pivot axle, a pair of support pins forengaging the upper and lower ends of the assembly, and a bias member forbiasing the fixture about the pivot axle and the assembly intoengagement with the rotary mechanism; a single laser beam that isaxially spaced apart from the fixture and the assembly for projectinglight into the openings between the components of the assembly; andwherein the rotary mechanism rotates the assembly relative to thefixture while the fixture is stationary, and an entire circumferentiallength of the openings and the photosetting substance in the openingsare exposed to the light in order to cure the photosetting substancelocated inside the assembly.